1. Field of the Invention
The present invention relates generally to a process for adding an organic compound to coolant water in a pressurized water reactor, and more particularly, for adding the organic compound to coolant water passing through a primary circuit of the pressurized water reactor.
2. Background of the Invention
Crud is the result of corrosion products formed when structural materials in the primary circuit, e.g., Reactor Coolant System (RCS), are exposed to coolant water, e.g., reactor coolant, during plant operation. These corrosion products are subsequently released into the coolant and can then deposit on the fuel in the reactor core. As core crud deposit thickness increases, heat transfer decreases as compared to the heat transfer of a clean surface. The temperature at the heat transfer surface will rise, increasing cladding corrosion. Minimizing fuel cladding corrosion is important to assure cladding integrity for all periods of plant operation. It is also an important consideration in fuel rod and reactor core design. Historically, significant effort has been expended in selection of corrosion resistant materials and in development of chemistry control additives and plant operating practices to minimize crud formation and crud deposition in the reactor core.
Crud induced power shift (CIPS) can occur when boron, which is present as boric acid, a reactor coolant additive used to control reactivity in a commercial nuclear power plant, such as, a pressurized water reactor (PWR), accumulates to sufficiently high concentrations within core crud deposits to suppress local neutron flux. This results in a shift in axial power distribution away from the boron deposits. The occurrence of CIPS during power operation at various commercial PWRs has been attributed to sufficiently thick, localized corrosion product deposits in the upper spans of a PWR core coincident with locations where the highest reaction steaming rates are predicted to occur. Locally thick crud deposits can also reduce heat transfer and increase fuel cladding temperatures which can lead to crud induced localized corrosion (CILC) and possibly fuel failures.
The injection of a soluble zinc additive to the reactor coolant of PWRs has been used for the purpose of radiation field reduction, general corrosion control, and primary water stress corrosion cracking (PWSCC) mitigation. In the PWR system, water is used as the reactor coolant. The water is circulated by pumps through-out a primary circuit, i.e., the RCS, that includes a pressure vessel which houses the heat generating reactor core, and a plurality of flow loops. The water in the primary circuit normally contains boric acid to control reactivity, hydrogen to provide reducing conditions, and an additive to maintain pH in a target control band. When “zinc addition” has been employed at a PWR, zinc acetate has been the preferred additive that is added to the reactor coolant. The use of zinc acetate was desirable because the acetate anion allowed for the zinc to be provided in a soluble form, and the anion and its decomposition products exhibited minimal or no detrimental effect on materials of construction in the RCS. The addition of zinc in the form of soluble zinc acetate has been utilized at a number of commercial PWR power plants.
As a result of adding zinc acetate to the reactor coolant of PWRs, desirable changes have been observed in ex-core shutdown radiation fields and various characteristics of core crud deposits. However, zinc acetate addition may result in various operation and/or design challenges. There is a desire to find a reactor coolant additive that can be added to the coolant water to produce elemental carbon. Further, there is a desire to find a reactor coolant additive that can condition core crud deposits. Moreover, there is a desire to find a reactor coolant additive to produce beneficial changes in the deposition and morphology of crud deposits without the potential challenges of known additives. Such an additive would be desirable for use in a wide variety of power plants, worldwide that utilize water reactor core designs.
Thus, it is further desired to develop a process for conditioning core crud deposits that results in core crud deposits having at least one of the following features: (i) a change in morphology, e.g., crud is finer grained and/or less well-crystallized, (ii) a change in deposition pattern, e.g., the crud is thinner and/or more uniformly distributed, (iii) a decrease in residence time, e.g., the crud has a shorter residence time on the core, and (iv) a change in composition, e.g., the crud has a higher carbon content. Furthermore, it is desired to develop a process that can inhibit CIPS, and/or CILC, and/or general cladding corrosion and/or fuel failures in water reactors.